Pb–S coordination triggering the methylthio SAM for thermal stability of inverted perovskite solar cells over 5000 h

Thermal stability acts as the core determinant of the operational lifespan of perovskite solar cells, and thermal degradation mainly stems from severe nonradiative recombination triggered by interfacial defects and thermally induced lattice strain. Conventional oxygen-containing passivation agents merely form fragile, thermally labile Pb–O bonds that readily dissociate under high-temperature conditions. Guided by the hard and soft acids and bases (HSAB) theory, we rationally design a methylthio-substituted cyanovinylphosphonic acid self-assembled monolayer (MeS-PCPA) to construct robust Pb–S coordination networks at the buried NiO_x/perovskite interface, which form the strong and stable Pb–S coordination interactions at the interface. These Pb–S coordination interactions exert dual synergistic effects: they optimize interfacial energy level alignment to suppress nonradiative energy losses, and simultaneously regulate perovskite crystallization to produce light-absorbing layers with an ultralow defect density. Such strong chemical coordination suppresses deep-level trap states, mitigates thermal lattice distortion, and enhances hole transport capacity. Solar devices modified with this SAM achieve a power conversion efficiency (PCE) of 26.29%. In addition, unencapsulated devices retained 95% of their initial efficiency after 5000 hours (ISOS-T-1) of thermal aging.